Quantum well infrared photodetector and method for fabricating same

ABSTRACT

High quality epitaxial layers of monocrystalline materials can be grown overlying monocrystalline substrates such as large silicon wafers by forming a compliant substrate for growing the monocrystalline layers. One way to achieve the formation of a compliant substrate includes first growing an accommodating buffer layer ( 204 ) on a silicon wafer ( 202 ). The accommodating buffer layer is a layer of monocrystalline oxide spaced apart from the silicon wafer by an amorphous interface layer ( 206 ) of silicon oxide. The amorphous interface layer dissipates strain and permits the growth of a high quality monocrystalline oxide accommodating buffer layer. The accommodating buffer layer is lattice matched to both the underlying silicon wafer and the overlying monocrystalline layer. Any lattice mismatch between the accommodating buffer layer and the underlying silicon substrate is taken care of by the amorphous interface layer. In addition, formation of a compliant substrate may include utilizing surfactant enhanced epitaxy, epitaxial growth of single crystal silicon onto single crystal oxide, and epitaxial growth of Zintl phase materials. Quantum well infrared photodetectors ( 200 ) can be grown on the high quality epitaxial monocrystalline material formed on such compliant substrates to create highly reliable devices having reduced costs.

FIELD OF THE INVENTION

[0001] This invention relates generally to semiconductor structures anddevices and to a method for their fabrication, and more specifically tomultiple quantum well infrared photodetectors formed using Group III-Vand/or Group II-VI periodic table material combinations grown on acompliant substrate.

BACKGROUND OF THE INVENTION

[0002] Semiconductor devices typically include multiple layers ofconductive, insulating, and semiconductive layers. Often, the desirableproperties of such layers improve with the crystallinity of the layer.For example, the electron mobility and band gap of semiconductive layersimproves as the crystallinity of the layer increases. Similarly, thefree electron concentration of conductive layers and the electron chargedisplacement and electron energy recoverability of insulative ordielectric films improves as the crystallinity of these layersincreases.

[0003] For many years, attempts have been made to grow variousmonolithic thin films on a foreign substrate, such as silicon (Si). Toachieve optimal characteristics of the various monolithic layers,however, a monocrystalline film of high crystalline quality is desired.Attempts have been made, for example, to grow various monocrystallinelayers on a substrate such as germanium, silicon, and variousinsulators. These attempts have generally been unsuccessful becauselattice mismatches between the host crystal and the grown crystal havecaused the resulting layer of monocrystalline material to be of lowcrystalline quality.

[0004] If a large area thin film of high quality monocrystallinematerial was available at low cost, a variety of semiconductor devicescould advantageously be fabricated in that film at a low cost comparedto the cost of fabricating such devices beginning with a bulk wafer ofsemiconductor material or in an epitaxial film of such material on abulk wafer of semiconductor material. In addition, if a thin film ofhigh quality monocrystalline material could be realized beginning with abulk wafer such as a silicon wafer, an integrated device structure couldbe achieved that took advantage of the best properties of both thesilicon and the high quality monocrystalline material.

[0005] Accordingly, a need exists for a semiconductor structure thatprovides a high quality monocrystalline film or layer over anothermonocrystalline material and for a process for making such a structure.

[0006] This structure and process could have extensive applications. Onesuch application of this structure and process involves the formation ofquantum well infrared photodetectors. Recently, multi-quantum wellstructures built using multiple layers of semiconductor materials withalternating band gaps have proven to be applicable in building quantumwell infrared photodetectors (QWIPs). An advantage of QWIPs is that theyhave the ability to sense multiple wavelengths of radiation and outputcurrent according to the wavelength absorbed. However, present-day QWIPsare expensive due to high-cost substrates and the requirement ofseparate CMOS circuits required to sense the output of each QWIP arrayelement.

[0007] Accordingly, a need exists for a low cost quantum well infraredphotodetector and a process for making the same.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention is illustrated by way of example and notlimitation in the accompanying figures, in which like referencesindicate similar elements, and in which:

[0009] FIGS. 1-3 illustrate schematically, in cross section, devicestructures in accordance with various embodiments of the invention;

[0010]FIG. 4 illustrates graphically the relationship between maximumattainable film thickness and lattice mismatch between a host crystaland a grown crystalline overlayer;

[0011]FIG. 5 illustrates a high resolution Transmission ElectronMicrograph of a structure including a monocrystalline accommodatingbuffer layer;

[0012]FIG. 6 illustrates an x-ray diffraction spectrum of a structureincluding a monocrystalline accommodating buffer layer;

[0013]FIG. 7 illustrates a high resolution Transmission ElectronMicrograph of a structure including an amorphous oxide layer;

[0014]FIG. 8 illustrates an x-ray diffraction spectrum of a structureincluding an amorphous oxide layer;

[0015] FIGS. 9A-9D illustrate schematically, in cross-section, theformation of a device structure in accordance with another embodiment ofthe invention;

[0016] FIGS. 10-10D illustrate a probable molecular bonding structure ofthe device structures illustrated in FIGS. 9A-9D;

[0017] FIGS. 11-13 illustrate schematically, in cross-section, theformation of yet another embodiment of a device structure in accordancewith the invention; and

[0018]FIG. 14 illustrates schematically, in cross-section, an exemplaryembodiment of a quantum well infrared photodetector fabricated on asemiconductor substrate according to the present invention.

[0019] Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020]FIG. 1 illustrates schematically, in cross section, a portion of asemiconductor structure 20 in accordance with an embodiment of theinvention. Semiconductor structure 20 includes a monocrystallinesubstrate 22, accommodating buffer layer 24 comprising a monocrystallinematerial, and a monocrystalline material layer 26. In this context, theterm “monocrystalline”shall have the meaning commonly used within thesemiconductor industry. The term shall refer to materials that are asingle crystal or that are substantially a single crystal and shallinclude those materials having a relatively small number of defects suchas dislocations and the like as are commonly found in substrates ofsilicon or germanium or mixtures of silicon and germanium and epitaxiallayers of such materials commonly found in the semiconductor industry.

[0021] In accordance with one embodiment of the invention, structure 20also includes an amorphous intermediate layer 28 positioned betweensubstrate 22 and accommodating buffer layer 24. Structure 20 may alsoinclude a template layer 30 between the accommodating buffer layer andmonocrystalline material layer 26. As will be explained more fullybelow, the template layer helps to initiate the growth of themonocrystalline material layer on the accommodating buffer layer. Theamorphous intermediate layer helps to relieve the strain in theaccommodating buffer layer and by doing so, aids in the growth of a highcrystalline quality accommodating buffer layer.

[0022] Substrate 22, in accordance with an embodiment of the invention,is a monocrystalline semiconductor or compound semiconductor wafer,preferably of large diameter. The wafer can be of, for example, amaterial from Group IV of the periodic table, and preferably a materialfrom Group IVA. Examples of Group IV semiconductor materials includesilicon, germanium, mixed silicon and germanium, mixed silicon andcarbon, mixed silicon, germanium and carbon, and the like. Preferablysubstrate 22 is a wafer containing silicon or germanium, and mostpreferably is a high quality monocrystalline silicon wafer as used inthe semiconductor industry. Accommodating buffer layer 24 is preferablya monocrystalline oxide or nitride material epitaxially grown on theunderlying substrate. In accordance with one embodiment of theinvention, amorphous intermediate layer 28 is grown on substrate 22 atthe interface between substrate 22 and the growing accommodating bufferlayer by the oxidation of substrate 22 during the growth of layer 24.The amorphous intermediate layer serves to relieve strain that mightotherwise occur in the monocrystalline accommodating buffer layer as aresult of differences in the lattice constants of the substrate and thebuffer layer. As used herein, lattice constant refers to the distancebetween atoms of a cell measured in the plane of the surface. If suchstrain is not relieved by the amorphous intermediate layer, the strainmay cause defects in the crystalline structure of the accommodatingbuffer layer. Defects in the crystalline structure of the accommodatingbuffer layer, in turn, would make it difficult to achieve a high qualitycrystalline structure in monocrystalline material layer 26, which maycomprise a semiconductor material, a compound semiconductor material, oranother type of material such as a metal or a non-metal.

[0023] Accommodating buffer layer 24 is preferably a monocrystallineoxide or nitride material selected for its crystalline compatibilitywith the underlying substrate and with the overlying material layer. Forexample, the material could be an oxide or nitride having a latticestructure matched to the substrate and to the subsequently appliedmonocrystalline material layer. Materials that are suitable for theaccommodating buffer layer include metal oxides such as the alkalineearth metal titanates, alkaline earth metal zirconates, alkaline earthmetal hafnates, alkaline earth metal tantalates, alkaline earth metalruthenates, alkaline earth metal niobates, alkaline earth metalvanadates, perovskite oxides such as alkaline earth metal tin-basedperovskites, lanthanum aluminate, lanthanum scandium oxide, andgadolinium oxide. Additionally, various nitrides such as galliumnitride, aluminum nitride, and boron nitride may also be used for theaccommodating buffer layer. Most of these materials are insulators,although strontium ruthenate, for example, is a conductor. Generally,these materials are metal oxides or metal nitrides, and moreparticularly, these metal oxide or nitrides typically include at leasttwo different metallic elements. In some specific applications, themetal oxides or nitride may include three or more different metallicelements.

[0024] Amorphous interface layer 28 is preferably an oxide formed by theoxidation of the surface of substrate 22, and more preferably iscomposed of a silicon oxide. The thickness of layer 28 is sufficient torelieve strain attributed to mismatches between the lattice constants ofsubstrate 22 and accommodating buffer layer 24. Typically, layer 28 hasa thickness in the range of approximately 0.5-5 nm.

[0025] The material for monocrystalline material layer 26 can beselected, as desired, for a particular structure or application. Forexample, the monocrystalline material of layer 26 may comprise acompound semiconductor which can be selected, as needed for a particularsemiconductor structure, from any of the Group IIIA and VA elements(III-V semiconductor compounds), mixed III-V compounds, Group II(A or B)and VIA elements (II-VI semiconductor compounds), and mixed II-VIcompounds. Examples include gallium arsenide (GaAs), gallium indiumarsenide (GaInAs), gallium aluminum arsenide (GaAlAs), indium phosphide(InP), cadmium sulfide (CdS), cadmium mercury telluride (CdHgTe), zincselenide (ZnSe), zinc sulfur selenide (ZnSSe), and the like. However,monocrystalline material layer 26 may also comprise other semiconductormaterials, metals, or non-metal materials which are used in theformation of semiconductor structures, devices and/or integratedcircuits.

[0026] Appropriate materials for template 30 are discussed below.Suitable template materials chemically bond to the surface of theaccommodating buffer layer 24 at selected sites and provide sites forthe nucleation of the epitaxial growth of monocrystalline material layer26. When used, template layer 30 has a thickness ranging from about 1 toabout 10 monolayers.

[0027]FIG. 2 illustrates, in cross section, a portion of a semiconductorstructure 40 in accordance with a further embodiment of the invention.Structure 40 is similar to the previously described semiconductorstructure 20, except that an additional buffer layer 32 is positionedbetween accommodating buffer layer 24 and monocrystalline material layer26. Specifically, the additional buffer layer is positioned betweentemplate layer 30 and the overlying layer of monocrystalline material.The additional buffer layer, formed of a semiconductor or compoundsemiconductor material when the monocrystalline material layer 26comprises a semiconductor or compound semiconductor material, serves toprovide a lattice compensation when the lattice constant of theaccommodating buffer layer cannot be adequately matched to the overlyingmonocrystalline semiconductor or compound semiconductor material layer.

[0028]FIG. 3 schematically illustrates, in cross section, a portion of asemiconductor structure 34 in accordance with another exemplaryembodiment of the invention. Structure 34 is similar to structure 20,except that structure 34 includes an amorphous layer 36, rather thanaccommodating buffer layer 24 and amorphous interface layer 28, and anadditional monocrystalline layer 38.

[0029] As explained in greater detail below, amorphous layer 36 may beformed by first forming an accommodating buffer layer and an amorphousinterface layer in a similar manner to that described above.Monocrystalline layer 38 is then formed (by epitaxial growth) overlyingthe monocrystalline accommodating buffer layer. The accommodating bufferlayer is then exposed to an anneal process to convert themonocrystalline accommodating buffer layer to an amorphous layer.Amorphous layer 36 formed in this manner comprises materials from boththe accommodating buffer and interface layers, which amorphous layersmay or may not amalgamate. Thus, layer 36 may comprise one or twoamorphous layers. Formation of amorphous layer 36 between substrate 22and additional monocrystalline layer 26 (subsequent to layer 38formation) relieves stresses between layers 22 and 38 and provides atrue compliant substrate for subsequent processing—e.g., monocrystallinematerial layer 26 formation.

[0030] The processes previously described above in connection with FIGS.1 and 2 are adequate for growing monocrystalline material layers over amonocrystalline substrate. However, the process described in connectionwith FIG. 3, which includes transforming a monocrystalline accommodatingbuffer layer to an amorphous oxide layer, may be better for growingmonocrystalline material layers because it allows any strain in layer 26to relax.

[0031] Additional monocrystalline layer 38 may include any of thematerials described throughout this application in connection witheither of monocrystalline material layer 26 or additional buffer layer32. For example, when monocrystalline material layer 26 comprises asemiconductor or compound semiconductor material, layer 38 may includemonocrystalline Group IV or monocrystalline compound semiconductormaterials.

[0032] In accordance with one embodiment of the present invention,additional monocrystalline layer 38 serves as an anneal cap during layer36 formation and as a template for subsequent monocrystalline layer 26formation. Accordingly, layer 38 is preferably thick enough to provide asuitable template for layer 26 growth (at least one monolayer) and thinenough to allow layer 38 to form as a substantially defect freemonocrystalline material.

[0033] In accordance with another embodiment of the invention,additional monocrystalline layer 38 comprises monocrystalline material(e.g., a material discussed above in connection with monocrystallinelayer 26) that is thick enough to form devices within layer 38. In thiscase, a semiconductor structure in accordance with the present inventiondoes not include monocrystalline material layer 26. In other words, thesemiconductor structure in accordance with this embodiment only includesone monocrystalline layer disposed above amorphous oxide layer 36.

[0034] The following non-limiting, illustrative examples illustratevarious combinations of materials useful in structures 20, 40, and 34 inaccordance with various alternative embodiments of the invention. Theseexamples are merely illustrative, and it is not intended that theinvention be limited to these illustrative examples.

EXAMPLE 1

[0035] In accordance with one embodiment of the invention,monocrystalline substrate 22 is a silicon substrate oriented in the(100) direction. The silicon substrate can be, for example, a siliconsubstrate as is commonly used in making complementary metal oxidesemiconductor (CMOS) integrated circuits having a diameter of about200-300 mm. In accordance with this embodiment of the invention,accommodating buffer layer 24 is a monocrystalline layer ofSr_(z)Ba_(1−z)TiO₃ where z ranges from 0 to 1 and the amorphousintermediate layer is a layer of silicon oxide (SiO_(x)) formed at theinterface between the silicon substrate and the accommodating bufferlayer. The value of z is selected to obtain one or more latticeconstants closely matched to corresponding lattice constants of thesubsequently formed layer 26. The accommodating buffer layer can have athickness of about 2 to about 100 nanometers (nm) and preferably has athickness of about 5 nm. In general, it is desired to have anaccommodating buffer layer thick enough to isolate the compoundsemiconductor layer from the substrate to obtain the desired electricaland optical properties. Layers thicker than 100 nm usually providelittle additional benefit while increasing cost unnecessarily; however,thicker layers may be fabricated if needed. The amorphous intermediatelayer of silicon oxide can have a thickness of about 0.5-5 nm, andpreferably a thickness of about 1-2 nm.

[0036] In accordance with this embodiment of the invention,monocrystalline material layer 26 is a compound semiconductor layer ofgallium arsenide (GaAs) or aluminum gallium arsenide (AlGaAs) having athickness of about 1 nm to about 100 micrometers (μm) and preferably athickness of about 0.5 μm to 10 μm. The thickness generally depends onthe application for which the layer is being prepared. To facilitate theepitaxial growth of the gallium arsenide or aluminum gallium arsenide onthe monocrystalline oxide, a template layer is formed by capping theoxide layer. The template layer is preferably 1-10 monolayers of Ti—As,Sr—O—As, Sr—Ga—O, or Sr—Al—O. By way of a preferred example, 1-2monolayers of Ti—As or Sr—Ga—O have been shown to successfully grow GaAslayers.

EXAMPLE 2

[0037] In accordance with a further embodiment of the inventionmonocrystalline substrate 22 is a silicon substrate as described above.The accommodating buffer layer is a monocrystalline oxide of strontiumor barium zirconate or hafnate in a cubic or orthorhombic phase with anamorphous intermediate layer of silicon oxide formed at the interfacebetween the silicon substrate and the accommodating buffer layer. Theaccommodating buffer layer can have a thickness of about 2-100 nm andpreferably has a thickness of at least 5 nm to ensure adequatecrystalline and surface quality and is formed of a monocrystallineSrZrO₃, BaZrO₃, SrHfO₃, BaSnO₃ or BaHfO₃. For example, a monocrystallineoxide layer of BaZrO₃ can grow at a temperature of about 700 degrees C.The lattice structure of the resulting crystalline oxide exhibits a 45degree rotation with respect to the substrate silicon lattice structure.

[0038] An accommodating buffer layer formed of these zirconate orhafnate materials is suitable for the growth of a monocrystallinematerial layer which comprises compound semiconductor materials in theindium phosphide (InP) system. In this system, the compoundsemiconductor material can be, for example, indium phosphide (InP),indium gallium arsenide (InGaAs), aluminum indium arsenide, (AlInAs), oraluminum gallium indium arsenic phosphide (AlGaInAsP), having athickness of about 1.0 nm to 10 μm. A suitable template for thisstructure is 1-10 monolayers of zirconium-arsenic (Zr—As),zirconium-phosphorus (Zr—P), hafnium-arsenic (Hf—As), hafnium-phosphorus(Hf—P), strontium-oxygen-arsenic (Sr—O—As), strontium-oxygen-phosphorus(Sr—O—P), barium-oxygen-arsenic (Ba—O—As), indium-strontium-oxygen(In—Sr—O), or barium-oxygen-phosphorus (Ba—O—P), and preferably 1-2monolayers of one of these materials. By way of an example, for a bariumzirconate accommodating buffer layer, the surface is terminated with 1-2monolayers of zirconium followed by deposition of 1-2 monolayers ofarsenic to form a Zr—As template. A monocrystalline layer of thecompound semiconductor material from the indium phosphide system is thengrown on the template layer. The resulting lattice structure of thecompound semiconductor material exhibits a 45 degree rotation withrespect to the accommodating buffer layer lattice structure and alattice mismatch to (100) InP of less than 2.5%, and preferably lessthan about 1.0%.

EXAMPLE 3

[0039] In accordance with a further embodiment of the invention, astructure is provided that is suitable for the growth of an epitaxialfilm of a monocrystalline material comprising a II-VI material overlyinga silicon substrate. The substrate is preferably a silicon wafer asdescribed above. A suitable accommodating buffer layer material isSr_(x)Ba_(1−x)TiO₃, where x ranges from 0 to 1, having a thickness ofabout 2-100 nm and preferably a thickness of about 5-15 nm. Where themonocrystalline layer comprises a compound semiconductor material, theII-VI compound semiconductor material can be, for example, zinc selenide(ZnSe) or zinc sulfur selenide (ZnSSe). A suitable template for thismaterial system includes 1-10 monolayers of zinc-oxygen (Zn—O) followedby 1-2 monolayers of an excess of zinc followed by the selenidation ofzinc on the surface. Alternatively, a template can be, for example, 1-10monolayers of strontium-sulfur (Sr—S) followed by the ZnSeS.

EXAMPLE 4

[0040] This embodiment of the invention is an example of structure 40illustrated in FIG. 2. Substrate 22, accommodating buffer layer 24, andmonocrystalline material layer 26 can be similar to those described inexample 1. In addition, an additional buffer layer 32 serves toalleviate any strains that might result from a mismatch of the crystallattice of the accommodating buffer layer and the lattice of themonocrystalline semiconductor material. Buffer layer 32 can be a layerof germanium or a GaAs, an aluminum gallium arsenide (AlGaAs), an indiumgallium phosphide (InGaP), an aluminum gallium phosphide (AlGaP), anindium gallium arsenide (InGaAs), an aluminum indium phosphide (AlInP),a gallium arsenide phosphide (GaAsP), or an indium gallium phosphide(InGaP) strain compensated superlattice. In accordance with one aspectof this embodiment, buffer layer 32 includes a GaAs_(x)P_(1−x)superlattice, wherein the value of x ranges from 0 to 1. In accordancewith another aspect, buffer layer 32 includes an In_(y)Ga_(1−y)Psuperlattice, wherein the value of y ranges from 0 to 1. By varying thevalue of x or y, as the case may be, the lattice constant is varied frombottom to top across the superlattice to create a match between latticeconstants of the underlying oxide and the overlying monocrystallinematerial which in this example is a compound semiconductor material. Thecompositions of other compound semiconductor materials, such as thoselisted above, may also be similarly varied to manipulate the latticeconstant of layer 32 in a like manner. The superlattice can have athickness of about 50-500 nm and preferably has a thickness of about100-200 nm. The template for this structure can be the same of thatdescribed in example 1. Alternatively, buffer layer 32 can be a layer ofmonocrystalline germanium having a thickness of 1-50 nm and preferablyhaving a thickness of about 2-20 nm. In using a germanium buffer layer,a template layer of either germanium-strontium (Ge—Sr) orgermanium-titanium (Ge—Ti) having a thickness of about one monolayer canbe used as a nucleating site for the subsequent growth of themonocrystalline material layer which in this example is a compoundsemiconductor material. The formation of the oxide layer is capped witheither a monolayer of strontium or a monolayer of titanium to act as anucleating site for the subsequent deposition of the monocrystallinegermanium. The monolayer of strontium or titanium provides a nucleatingsite to which the first monolayer of germanium can bond.

EXAMPLE 5

[0041] This example also illustrates materials useful in a structure 40as illustrated in FIG. 2. Substrate material 22, accommodating bufferlayer 24, monocrystalline material layer 26 and template layer 30 can bethe same as those described above in example 2. In addition, additionalbuffer layer 32 is inserted between the accommodating buffer layer andthe overlying monocrystalline material layer. The buffer layer, afurther monocrystalline material which in this instance comprises asemiconductor material, can be, for example, a graded layer of indiumgallium arsenide (InGaAs) or indium aluminum arsenide (InAlAs). Inaccordance with one aspect of this embodiment, additional buffer layer32 includes InGaAs, in which the indium composition varies from 0 toabout 50%. The buffer layer preferably has a thickness of about 10-30nm. Varying the composition of the buffer layer from GaAs to InGaAsserves to provide a lattice match between the underlying monocrystallineoxide material and the overlying layer of monocrystalline material whichin this example is a compound semiconductor material. Such a bufferlayer is especially advantageous if there is a lattice mismatch betweenaccommodating buffer layer 24 and monocrystalline material layer 26.

EXAMPLE 6

[0042] This example provides exemplary materials useful in structure 34,as illustrated in FIG. 3. Substrate material 22, template layer 30, andmonocrystalline material layer 26 may be the same as those describedabove in connection with example 1.

[0043] Amorphous layer 36 is an amorphous oxide layer which is suitablyformed of a combination of amorphous intermediate layer materials (e.g.,layer 28 materials as described above) and accommodating buffer layermaterials (e.g., layer 24 materials as described above). For example,amorphous layer 36 may include a combination of SiO_(x) andSr_(z)Ba_(1−z)TiO₃ (where z ranges from 0 to 1), which combine or mix,at least partially, during an anneal process to form amorphous oxidelayer 36.

[0044] The thickness of amorphous layer 36 may vary from application toapplication and may depend on such factors as desired insulatingproperties of layer 36, type of monocrystalline material comprisinglayer 26, and the like. In accordance with one exemplary aspect of thepresent embodiment, layer 36 thickness is about 2 nm to about 100 nm,preferably about 2-10 nm, and more preferably about 5-6 nm.

[0045] Layer 38 comprises a monocrystalline material that can be grownepitaxially over a monocrystalline oxide material such as material usedto form accommodating buffer layer 24. In accordance with one embodimentof the invention, layer 38 includes the same materials as thosecomprising layer 26. For example, if layer 26 includes GaAs, layer 38also includes GaAs. However, in accordance with other embodiments of thepresent invention, layer 38 may include materials different from thoseused to form layer 26. In accordance with one exemplary embodiment ofthe invention, layer 38 is about 1 monolayer to about 100 nm thick.

[0046] Referring again to FIGS. 1-3, substrate 22 is a monocrystallinesubstrate such as a monocrystalline silicon or gallium arsenidesubstrate. The crystalline structure of the monocrystalline substrate ischaracterized by a lattice constant and by a lattice orientation. Insimilar manner, accommodating buffer layer 24 is also a monocrystallinematerial and the lattice of that monocrystalline material ischaracterized by a lattice constant and a crystal orientation. Thelattice constants of the accommodating buffer layer and themonocrystalline substrate must be closely matched or, alternatively,must be such that upon rotation of one crystal orientation with respectto the other crystal orientation, a substantial match in latticeconstants is achieved. In this context the terms “substantially equal”and “substantially matched” mean that there is sufficient similaritybetween the lattice constants to permit the growth of a high qualitycrystalline layer on the underlying layer.

[0047]FIG. 4 illustrates graphically the relationship of the achievablethickness of a grown crystal layer of high crystalline quality as afunction of the mismatch between the lattice constants of the hostcrystal and the grown crystal. Curve 42 illustrates the boundary of highcrystalline quality material. The area to the right of curve 42represents layers that have a large number of defects. With no latticemismatch, it is theoretically possible to grow an infinitely thick, highquality epitaxial layer on the host crystal. As the mismatch in latticeconstants increases, the thickness of achievable, high qualitycrystalline layer decreases rapidly. As a reference point, for example,if the lattice constants between the host crystal and the grown layerare mismatched by more than about 2%, monocrystalline epitaxial layersin excess of about 20 nm cannot be achieved.

[0048] In accordance with one embodiment of the invention, substrate 22is a (100) or (111) oriented monocrystalline silicon wafer andaccommodating buffer layer 24 is a layer of strontium barium titanate.Substantial matching of lattice constants between these two materials isachieved by rotating the crystal orientation of the titanate material by45° with respect to the crystal orientation of the silicon substratewafer. The inclusion in the structure of amorphous interface layer 28, asilicon oxide layer in this example, if it is of sufficient thickness,serves to reduce strain in the titanate monocrystalline layer that mightresult from any mismatch in the lattice constants of the host siliconwafer and the grown titanate layer. As a result, in accordance with anembodiment of the invention, a high quality, thick, monocrystallinetitanate layer is achievable.

[0049] Still referring to FIGS. 1-3, layer 26 is a layer of epitaxiallygrown monocrystalline material and that crystalline material is alsocharacterized by a crystal lattice constant and a crystal orientation.In accordance with one embodiment of the invention, the lattice constantof layer 26 differs from the lattice constant of substrate 22. Toachieve high crystalline quality in this epitaxially grownmonocrystalline layer, the accommodating buffer layer must be of highcrystalline quality. In addition, in order to achieve high crystallinequality in layer 26, substantial matching between the crystal latticeconstant of the host crystal, in this case, the monocrystallineaccommodating buffer layer, and the grown crystal is desired. Withproperly selected materials this substantial matching of latticeconstants is achieved as a result of rotation of the crystal orientationof the grown crystal with respect to the orientation of the hostcrystal. For example, if the grown crystal is gallium arsenide, aluminumgallium arsenide, zinc selenide, or zinc sulfur selenide and theaccommodating buffer layer is monocrystalline Sr_(x)Ba_(1−x)TiO₃,substantial matching of crystal lattice constants of the two materialsis achieved, wherein the crystal orientation of the grown layer isrotated by 45° with respect to the orientation of the hostmonocrystalline oxide. Similarly, if the host material is a strontium orbarium zirconate or a strontium or barium hafnate or barium tin oxideand the compound semiconductor layer is indium phosphide or galliumindium arsenide or aluminum indium arsenide, substantial matching ofcrystal lattice constants can be achieved by rotating the orientation ofthe grown crystal layer by 45° with respect to the host oxide crystal.In some instances, a crystalline semiconductor buffer layer between thehost oxide and the grown monocrystalline material layer can be used toreduce strain in the grown monocrystalline material layer that mightresult from small differences in lattice constants. Better crystallinequality in the grown monocrystalline material layer can thereby beachieved.

[0050] The following example illustrates a process, in accordance withone embodiment of the invention, for fabricating a semiconductorstructure such as the structures depicted in FIGS. 1-3. The processstarts by providing a monocrystalline semiconductor substrate comprisingsilicon or germanium. In accordance with a preferred embodiment of theinvention, the semiconductor substrate is a silicon wafer having a (100)orientation. The substrate is preferably oriented on axis or, at most,about 4° off axis. At least a portion of the semiconductor substrate hasa bare surface, although other portions of the substrate, as describedbelow, may encompass other structures. The term “bare” in this contextmeans that the surface in the portion of the substrate has been cleanedto remove any oxides, contaminants, or other foreign material. As iswell known, bare silicon is highly reactive and readily forms a nativeoxide. The term “bare” is intended to encompass such a native oxide. Athin silicon oxide may also be intentionally grown on the semiconductorsubstrate, although such a grown oxide is not essential to the processin accordance with the invention. In order to epitaxially grow amonocrystalline oxide layer overlying the monocrystalline substrate, thenative oxide layer must first be removed to expose the crystallinestructure of the underlying substrate. The following process ispreferably carried out by molecular beam epitaxy (MBE), although otherepitaxial processes may also be used in accordance with the presentinvention. The native oxide can be removed by first thermally depositinga thin layer of strontium, barium, a combination of strontium andbarium, or other alkali earth metals or combinations of alkali earthmetals in an MBE apparatus. In the case where strontium is used, thesubstrate is then heated to a temperature of about 850° C. to cause thestrontium to react with the native silicon oxide layer. The strontiumserves to reduce the silicon oxide to leave a silicon oxide-freesurface. The resultant surface, which exhibits an ordered 2×1 structure,includes strontium, oxygen, and silicon. The ordered 2×1 structure formsa template for the ordered growth of an overlying layer of amonocrystalline oxide. The template provides the necessary chemical andphysical properties to nucleate the crystalline growth of an overlyinglayer.

[0051] In accordance with an alternate embodiment of the invention, thenative silicon oxide can be converted and the substrate surface can beprepared for the growth of a monocrystalline oxide layer by depositingan alkali earth metal oxide, such as strontium oxide, strontium bariumoxide, or barium oxide, onto the substrate surface by MBE at a lowtemperature and by subsequently heating the structure to a temperatureof about 850° C. At this temperature a solid state reaction takes placebetween the strontium oxide and the native silicon oxide causing thereduction of the native silicon oxide and leaving an ordered 2×1structure with strontium, oxygen, and silicon remaining on the substratesurface. Again, this forms a template for the subsequent growth of anordered monocrystalline oxide layer.

[0052] Following the removal of the silicon oxide from the surface ofthe substrate, in accordance with one embodiment of the invention, thesubstrate is cooled to a temperature in the range of about 200-800° C.and a layer of strontium titanate is grown on the template layer bymolecular beam epitaxy. The MBE process is initiated by opening shuttersin the MBE apparatus to expose strontium, titanium and oxygen sources.The ratio of strontium and titanium is approximately 1:1. The partialpressure of oxygen is initially set at a minimum value to growstochiometric strontium titanate at a growth rate of about 0.3-0.5 nmper minute. After initiating growth of the strontium titanate, thepartial pressure of oxygen is increased above the initial minimum value.The overpressure of oxygen causes the growth of an amorphous siliconoxide layer at the interface between the underlying substrate and thegrowing strontium titanate layer. The growth of the silicon oxide layerresults from the diffusion of oxygen through the growing strontiumtitanate layer to the interface where the oxygen reacts with silicon atthe surface of the underlying substrate. The strontium titanate grows asan ordered monocrystal with the crystalline orientation rotated by 45°with respect to the ordered 2×1 crystalline structure of the underlyingsubstrate. Strain that otherwise might exist in the strontium titanatelayer because of the small mismatch in lattice constant between thesilicon substrate and the growing crystal is relieved in the amorphoussilicon oxide intermediate layer.

[0053] After the strontium titanate layer has been grown to the desiredthickness, the monocrystalline strontium titanate is capped by atemplate layer that is conducive to the subsequent growth of anepitaxial layer of a desired monocrystalline material. For example, forthe subsequent growth of a monocrystalline compound semiconductormaterial layer of gallium arsenide, the MBE growth of the strontiumtitanate monocrystalline layer can be capped by terminating the growthwith 1-2 monolayers of titanium, 1-2 monolayers of titanium-oxygen orwith 1-2 monolayers of strontium-oxygen. Following the formation of thiscapping layer, arsenic is deposited to form a Ti—As bond, a Ti—O—As bondor a Sr—O—As. Any of these form an appropriate template for depositionand formation of a gallium arsenide monocrystalline layer. Following theformation of the template, gallium is subsequently introduced to thereaction with the arsenic and gallium arsenide forms. Alternatively,gallium can be deposited on the capping layer to form a Sr—O—Ga bond,and arsenic is subsequently introduced with the gallium to form theGaAs.

[0054]FIG. 5 is a high resolution Transmission Electron Micrograph (TEM)of semiconductor material manufactured in accordance with one embodimentof the present invention. Single crystal SrTiO₃ accommodating bufferlayer 24 was grown epitaxially on silicon substrate 22. During thisgrowth process, amorphous interfacial layer 28 is formed which relievesstrain due to lattice mismatch. GaAs compound semiconductor layer 26 wasthen grown epitaxially using template layer 30.

[0055]FIG. 6 illustrates an x-ray diffraction spectrum taken on astructure including monocrystalline layer 26 comprising GaAs grown onsilicon substrate 22 using accommodating buffer layer 24. The peaks inthe spectrum indicate that both the accommodating buffer layer 24 andGaAs compound semiconductor layer 26 are single crystal and (100)orientated.

[0056] The structure illustrated in FIG. 2 can be formed by the processdiscussed above with the addition of an additional buffer layerdeposition step. The buffer layer is formed overlying the template layerbefore the deposition of the monocrystalline material layer. If thebuffer layer is a monocrystalline material layer comprising a compoundsemiconductor superlattice, such a superlattice can be deposited, by MBEfor example, on the template described above. If instead the bufferlayer is a monocrystalline material layer comprising a layer ofgermanium, the process above is modified to cap the strontium titanatemonocrystalline layer with a final layer of either strontium or titaniumand then by depositing germanium to react with the strontium ortitanium. The germanium buffer layer can then be deposited directly onthis template.

[0057] Structure 34, illustrated in FIG. 3, may be formed by growing anaccommodating buffer layer, forming an amorphous oxide layer oversubstrate 22, and growing semiconductor layer 38 over the accommodatingbuffer layer, as described above. The accommodating buffer layer and theamorphous oxide layer are then exposed to an anneal process sufficientto change the crystalline structure of the accommodating buffer layerfrom monocrystalline to amorphous, thereby forming an amorphous layersuch that the combination of the amorphous oxide layer and the nowamorphous accommodating buffer layer form a single amorphous oxide layer36. Layer 26 is then subsequently grown over layer 38. Alternatively,the anneal process may be carried out subsequent to growth of layer 26.

[0058] In accordance with one aspect of this embodiment, layer 36 isformed by exposing substrate 22, the accommodating buffer layer, theamorphous oxide layer, and monocrystalline layer 38 to a rapid thermalanneal process with a peak temperature of about 700° C. to about 1000°C. and a process time of about 5 seconds to about 10 minutes. However,other suitable anneal processes may be employed to convert theaccommodating buffer layer to an amorphous layer in accordance with thepresent invention. For example, laser annealing, electron beamannealing, or “conventional” thermal annealing processes (in the properenvironment) may be used to form layer 36. When conventional thermalannealing is employed to form layer 36, an overpressure of one or moreconstituents of layer 30 may be required to prevent degradation of layer38 during the anneal process. For example, when layer 38 includes GaAs,the anneal environment preferably includes an overpressure of arsenic tomitigate degradation of layer 38.

[0059] As noted above, layer 38 of structure 34 may include anymaterials suitable for either of layers 32 or 26. Accordingly, anydeposition or growth methods described in connection with either layer32 or 26, may be employed to deposit layer 38.

[0060]FIG. 7 is a high resolution Transmission Electron Micrograph (TEM)of semiconductor material manufactured in accordance with the embodimentof the invention illustrated in FIG. 3. In accordance with thisembodiment, a single crystal SrTiO₃ accommodating buffer layer was grownepitaxially on silicon substrate 22. During this growth process, anamorphous interfacial layer forms as described above. Next, additionalmonocrystalline layer 38 comprising a compound semiconductor layer ofGaAs is formed above the accommodating buffer layer and theaccommodating buffer layer is exposed to an anneal process to formamorphous oxide layer 36.

[0061]FIG. 8 illustrates an x-ray diffraction spectrum taken on astructure including additional monocrystalline layer 38 comprising aGaAs compound semiconductor layer and amorphous oxide layer 36 formed onsilicon substrate 22. The peaks in the spectrum indicate that GaAscompound semiconductor layer 38 is single crystal and (100) orientatedand the lack of peaks around 40 to 50 degrees indicates that layer 36 isamorphous.

[0062] The process described above illustrates a process for forming asemiconductor structure including a silicon substrate, an overlyingoxide layer, and a monocrystalline material layer comprising a galliumarsenide compound semiconductor layer by the process of molecular beamepitaxy. The process can also be carried out by the process of chemicalvapor deposition (CVD), metal organic chemical vapor deposition (MOCVD),migration enhanced epitaxy (MEE), atomic layer epitaxy (ALE), physicalvapor deposition (PVD), chemical solution deposition (CSD), pulsed laserdeposition (PLD), or the like. Further, by a similar process, othermonocrystalline accommodating buffer layers such as alkaline earth metaltitanates, zirconates, hafnates, tantalates, vanadates, ruthenates, andniobates, perovskite oxides such as alkaline earth metal tin-basedperovskites, lanthanum aluminate, lanthanum scandium oxide, andgadolinium oxide can also be grown. Further, by a similar process suchas MBE, other monocrystalline material layers comprising other III-V andII-VI monocrystalline compound semiconductors, semiconductors, metalsand non-metals can be deposited overlying the monocrystalline oxideaccommodating buffer layer.

[0063] Each of the variations of monocrystalline material layer andmonocrystalline oxide accommodating buffer layer uses an appropriatetemplate for initiating the growth of the monocrystalline materiallayer. For example, if the accommodating buffer layer is an alkalineearth metal zirconate, the oxide can be capped by a thin layer ofzirconium. The deposition of zirconium can be followed by the depositionof arsenic or phosphorus to react with the zirconium as a precursor todepositing indium gallium arsenide, indium aluminum arsenide, or indiumphosphide respectively. Similarly, if the monocrystalline oxideaccommodating buffer layer is an alkaline earth metal hafnate, the oxidelayer can be capped by a thin layer of hafnium. The deposition ofhafnium is followed by the deposition of arsenic or phosphorous to reactwith the hafnium as a precursor to the growth of an indium galliumarsenide, indium aluminum arsenide, or indium phosphide layer,respectively. In a similar manner, strontium titanate can be capped witha layer of strontium or strontium and oxygen and barium titanate can becapped with a layer of barium or barium and oxygen. Each of thesedepositions can be followed by the deposition of arsenic or phosphorusto react with the capping material to form a template for the depositionof a monocrystalline material layer comprising indium gallium arsenide,indium aluminum arsenide, or indium phosphide.

[0064] The formation of a device structure in accordance with anotherembodiment of the invention is illustrated schematically incross-section in FIGS. 9A-9D. Like the previously described embodimentsreferred to in FIGS. 1-3, this embodiment of the invention involves theprocess of forming a compliant substrate utilizing the epitaxial growthof single crystal oxides, such as the formation of accommodating bufferlayer 24 previously described with reference to FIGS. 1 and 2 andamorphous layer 36 previously described with reference to FIG. 3, andthe formation of a template layer 30. However, the embodimentillustrated in FIGS. 9A-9D utilizes a template that includes asurfactant to facilitate layer-by-layer monocrystalline material growth.

[0065] Turning now to FIG. 9A, an amorphous intermediate layer 58 isgrown on substrate 52 at the interface between substrate 52 and agrowing accommodating buffer layer 54, which is preferably amonocrystalline crystal oxide layer, by the oxidation of substrate 52during the growth of layer 54. Layer 54 is preferably a monocrystallineoxide material such as a monocrystalline layer of Sr_(z)Ba_(1−z)TiO₃where z ranges from 0 to 1. However, layer 54 may also comprise any ofthose compounds previously described with reference layer 24 in FIGS.1-2 and any of those compounds previously described with reference tolayer 36 in FIG. 3 which is formed from layers 24 and 28 referenced inFIGS. 1 and 2.

[0066] Layer 54 is grown with a strontium (Sr) terminated surfacerepresented in FIG. 9A by hatched line 55 which is followed by theaddition of a template layer 60 which includes a surfactant layer 61 andcapping layer 63 as illustrated in FIGS. 9B and 9C. Surfactant layer 61may comprise, but is not limited to, elements such as Al, In and Ga, butwill be dependent upon the composition of layer 54 and the overlyinglayer of monocrystalline material for optimal results. In one exemplaryembodiment, aluminum (Al) is used for surfactant layer 61 and functionsto modify the surface and surface energy of layer 54. Preferably,surfactant layer 61 is epitaxially grown, to a thickness of one to twomonolayers, over layer 54 as illustrated in FIG. 9B by way of molecularbeam epitaxy (MBE), although other epitaxial processes may also beperformed including chemical vapor deposition (CVD), metal organicchemical vapor deposition (MOCVD), migration enhanced epitaxy (MEE),atomic layer epitaxy (ALE), physical vapor deposition (PVD), chemicalsolution deposition (CSD), pulsed laser deposition (PLD), or the like.

[0067] Surfactant layer 61 is then exposed to a halogen such as arsenic,for example, to form capping layer 63 as illustrated in FIG. 9C.Surfactant layer 61 may be exposed to a number of materials to createcapping layer 63 such as elements which include, but are not limited to,As, P, Sb and N. Surfactant layer 61 and capping layer 63 combine toform template layer 60.

[0068] Monocrystalline material layer 66, which in this example is acompound semiconductor such as GaAs, is then deposited via MBE, CVD,MOCVD, MEE, ALE, PVD, CSD, PLD, and the like to form the final structureillustrated in FIG. 9D.

[0069] FIGS. 10A-10D illustrate possible molecular bond structures for aspecific example of a compound semiconductor structure formed inaccordance with the embodiment of the invention illustrated in FIGS.9A-9D. More specifically, FIGS. 10A-10D illustrate the growth of GaAs(layer 66) on the strontium terminated surface of a strontium titanatemonocrystalline oxide (layer 54) using a surfactant containing template(layer 60).

[0070] The growth of a monocrystalline material layer 66 such as GaAs onan accommodating buffer layer 54 such as a strontium titanium oxide overamorphous interface layer 58 and substrate layer 52, both of which maycomprise materials previously described with reference to layers 28 and22, respectively in FIGS. 1 and 2, illustrates a critical thickness ofabout 1000 Angstroms where the two-dimensional (2D) andthree-dimensional (3D) growth shifts because of the surface energiesinvolved. In order to maintain a true layer by layer growth (Frank Vander Mere growth), the following relationship must be satisfied:

δ_(STO)>(δ_(INT)+δ_(GaAs))

[0071] where the surface energy of the monocrystalline oxide layer 54must be greater than the surface energy of the amorphous interface layer58 added to the surface energy of the GaAs layer 66. Since it isimpracticable to satisfy this equation, a surfactant containing templatewas used, as described above with reference to FIGS. 9B-9D, to increasethe surface energy of the monocrystalline oxide layer 54 and also toshift the crystalline structure of the template to a diamond-likestructure that is in compliance with the original GaAs layer.

[0072]FIG. 10A illustrates the molecular bond structure of a strontiumterminated surface of a strontium titanate monocrystalline oxide layer.An aluminum surfactant layer is deposited on top of the strontiumterminated surface and bonds with that surface as illustrated in FIG.10B, which reacts to form a capping layer comprising a monolayer ofAl₂Sr having the molecular bond structure illustrated in FIG. 10B whichforms a diamond-like structure with an sp³ hybrid terminated surfacethat is compliant with compound semiconductors such as GaAs. Thestructure is then exposed to As to form a layer of AlAs as shown in FIG.10C. GaAs is then deposited to complete the molecular bond structureillustrated in FIG. 10D which has been obtained by 2D growth. The GaAscan be grown to any thickness for forming other semiconductorstructures, devices, or integrated circuits. Alkaline earth metals suchas those in Group IIA are those elements preferably used to form thecapping surface of the monocrystalline oxide layer 24 because they arecapable of forming a desired molecular structure with aluminum.

[0073] FIGS. 11-13 schematically illustrate, in cross-section, theformation of another embodiment of a device structure in accordance withthe invention. This embodiment includes a compliant layer that functionsas a transition layer that uses clathrate or Zintl type bonding. Morespecifically, this embodiment utilizes an intermetallic template layerto reduce the surface energy of the interface between material layersthereby allowing for two dimensional layer by layer growth.

[0074] The structure illustrated in FIG. 11 includes a monocrystallinesubstrate 102, an amorphous interface layer 108 and an accommodatingbuffer layer 104. Amorphous intermediate layer 108 is grown on substrate102 at the interface between substrate 102 and accommodating bufferlayer 104 as previously described with reference to FIGS. 1 and 2.Amorphous interface layer 108 may comprise any of those materialspreviously described with reference to amorphous interface layer 28 inFIGS. 1 and 2 but preferably comprises a monocrystalline oxide materialsuch as a monocrystalline layer of Sr_(z)Ba_(1−z)TiO₃ where z rangesfrom 0 to 1. Substrate 102 is preferably silicon but may also compriseany of those materials previously described with reference to substrate22 in FIGS. 1-3.

[0075] A template layer 130 is deposited over accommodating buffer layer104 as illustrated in FIG. 12 and preferably comprises a thin layer ofZintl type phase material composed of metals and metalloids having agreat deal of ionic character. As in previously described embodiments,template layer 130 is deposited by way of MBE, CVD, MOCVD, MEE, ALE,PVD, CSD, PLD, or the like to achieve a thickness of one monolayer.Template layer 130 functions as a “soft” layer with non-directionalbonding but high crystallinity which absorbs stress build up betweenlayers having lattice mismatch. Materials for template 130 may include,but are not limited to, materials containing Si, Ga, In, and Sb such as,for example, AlSr₂, (MgCaYb)Ga₂, (Ca, Sr, Eu, Yb)In₂, BaGe₂As, andSrSn₂As₂.

[0076] A monocrystalline material layer 126 is epitaxially grown overtemplate layer 130 to achieve the final structure illustrated in FIG.13. As a specific example, an SrAl₂ layer may be used as template layer130 and an appropriate monocrystalline material layer 126 such as acompound semiconductor material GaAs is grown over the SrAl₂. The Al—Ti(from the accommodating buffer layer of layer of Sr_(z)Ba¹⁻TiO₃ where zranges from 0 to 1) bond is mostly metallic while the Al—As (from theGaAs layer) bond is weakly covalent. The Sr participates in two distincttypes of bonding with part of its electric charge going to the oxygenatoms in the lower accommodating buffer layer 104 comprisingSr_(z)Ba_(1−z)TiO₃ to participate in ionic bonding and the other part ofits valence charge being donated to Al in a way that is typicallycarried out with Zintl phase materials. The amount of the chargetransfer depends on the relative electronegativity of elementscomprising the template layer 130 as well as on the interatomicdistance. In this example, Al assumes an sp³ hybridization and canreadily form bonds with monocrystalline material layer 126, which inthis example, comprises compound semiconductor material GaAs.

[0077] The compliant substrate produced by use of the Zintl typetemplate layer used in this embodiment can absorb a large strain withouta significant energy cost. In the above example, the bond strength ofthe Al is adjusted by changing the volume of the SrAl₂ layer therebymaking the device tunable for specific applications which include themonolithic integration of III-V and Si devices and the monolithicintegration of high-k dielectric materials for CMOS technology.

[0078] Clearly, those embodiments specifically describing structureshaving compound semiconductor portions and Group IV semiconductorportions, are meant to illustrate embodiments of the present inventionand not limit the present invention. There are a multiplicity of othercombinations and other embodiments of the present invention. Forexample, the present invention includes structures and methods forfabricating material layers which form semiconductor structures, devicesand integrated circuits including other layers such as metal andnon-metal layers. More specifically, the invention includes structuresand methods for forming a compliant substrate which is used in thefabrication of semiconductor structures, devices and integrated circuitsand the material layers suitable for fabricating those structures,devices, and integrated circuits. By using embodiments of the presentinvention, it is now simpler to integrate devices that includemonocrystalline layers comprising semiconductor and compoundsemiconductor materials as well as other material layers that are usedto form those devices with other components that work better or areeasily and/or inexpensively formed within semiconductor or compoundsemiconductor materials. This allows a device to be shrunk, themanufacturing costs to decrease, and yield and reliability to increase.

[0079] In accordance with one embodiment of this invention, amonocrystalline semiconductor or compound semiconductor wafer can beused in forming monocrystalline material layers over the wafer. In thismanner, the wafer is essentially a “handle” wafer used during thefabrication of semiconductor electrical components within amonocrystalline layer overlying the wafer. Therefore, electricalcomponents can be formed within semiconductor materials over a wafer ofat least approximately 200 millimeters in diameter and possibly at leastapproximately 300 millimeters.

[0080] By the use of this type of substrate, a relatively inexpensive“handle” wafer overcomes the fragile nature of compound semiconductor orother monocrystalline material wafers by placing them over a relativelymore durable and easy to fabricate base material. Therefore, anintegrated circuit can be formed such that all electrical components,and particularly all active electronic devices, can be formed within orusing the monocrystalline material layer even though the substrateitself may include a monocrystalline semiconductor material. Fabricationcosts for compound semiconductor devices and other devices employingnon-silicon monocrystalline materials should decrease because largersubstrates can be processed more economically and more readily comparedto the relatively smaller and more fragile substrates (e.g. conventionalcompound semiconductor wafers).

[0081] One application of the present invention includes the use ofsemiconductor structures described above in quantum well infraredphotodetectors (QWIPs). QWIPs are typically designed to detect infraredradiation at a particular wavelength and produce a current correspondingto the wavelength absorbed. Recently, multiple quantum well structuresusing multiple layers of semiconductor materials with alternating bandgaps have proven to be applicable in building QWIPs. These QWIPs arebased on a layered structure generally containing a plurality of GaAslayers alternating with a plurality of Al_(x)Ga_(1−x)As layers. AlthoughGaAs/Al_(x)Ga_(1−x)As has frequently been used in QWIPs, it will beappreciated that other materials, such asIn_(x)Ga_(1−x)As/In_(x)Al_(1−x)As, In_(x)Ga_(1−x)As/InP, InGaAs/InP andthe like, can also be used. A comprehensive description of the theoryand design of QWIPs is included in “Quantum-Well InfraredPhotodetectors,” J. Appl. Phys. 74(8), Oct. 15, 1993, by B. F. Levine.

[0082] An advantage of QWIPs is that they have the ability to sensemultiple wavelengths of radiation. They also take advantage of themature GaAs growth and processing technologies. However, conventionalQWIPs present several disadvantages, including the high cost ofsubstrate material used to manufacture the QWIPs and the need forseparate CMOS circuitry to sense the output of each element. Embodimentsof QWIPs of the present invention addresses these disadvantages by usinga standard silicon substrate and by coupling the QWIP structure with aconventional circuit to form a one chip solution for infrared detection.

[0083]FIG. 14 illustrates in cross section an exemplary embodiment of aQWIP 200 in accordance with the present invention. To fabricate QWIP200, a monocrystalline semiconductor substrate 202 such as siliconfunctions as the starting material. An accommodating buffer layer 204 isthen grown epitaxially over substrate 202 and an amorphous intermediatelayer 206 may be formed between substrate 202 and buffer layer 204 bythe oxidation of substrate 202 during the growth of buffer layer 204.Buffer layer 204 may be comprised of a monocrystalline oxide or nitridematerial such as that comprising layer 24, 54 and 104 with reference toFIGS. 1, 9 and 11, respectively. In accordance with one embodiment ofthe invention (not illustrated), a layer may comprise material fromamorphous oxide layer 206 and material from layer 204, which is formedby annealing amorphous intermediate layer 206 and buffer layer 204,forming a layer such as layer 36 described with reference to FIG. 3.

[0084] Next, an additional buffer layer 210 is deposited over bufferlayer 204. Additional buffer layer 210 may comprise materials such asthose comprising layer 32 with reference to FIG. 2 and having lowthermal conductivity properties. Alternatively, layer 210 may serve as atemplate layer formed of materials such as those comprising layer 60with reference to FIG. 9D, and layer 130 with reference to FIG. 13. Amonocrystalline material layer 208 is epitaxially deposited overadditional buffer layer 210. Additional buffer layer 210 serves toprovide a lattice compensation between buffer layer 204 andmonocrystalline material layer 208. Monocrystalline material layer 208may be comprised of a monocrystalline material such as that comprisinglayer 26 with reference to FIGS. 1, 2 and 3, layer 66 with reference toFIG. 9D, and layer 126 with reference to FIG. 13. A dopedmonocrystalline material layer 212 is epitaxially deposited overmonocrystalline material layer 208. Layer 212 preferably comprises adoped layer of materials from Groups III and V of the periodic table,such as n++GaAs.

[0085] A multiple quantum wells structure 214 is disposed on dopedmonocrystalline material layer 212. Each quantum well includes an activelayer 216 sandwiched between two barrier layers 218. Specific examplesof a QWIP described in FIG. 14 include a structure where quantum wellsinclude active layers 218 comprised of n++GaAs sandwiched betweenbarrier layers 218 which are comprised of Al_(x)Ga_(1−x)As, where xranges from about 0 to 1.0 and is preferably about 0.3. The thickness ofactive layers 218 preferably ranges from about 20 angstroms to 100angstroms and is more preferably about 50 angstroms. The thickness ofbarrier layers 218 preferably ranges from 400 angstroms to 800 angstromsand is preferably 500 angstroms.

[0086] An additional doped monocrystalline material layer 220 is thendeposited over multiple quantum wells structure 214. Layer 220 maycomprise the same materials as in layer 212 and preferably comprises adoped layer of materials from Groups III and V of the periodic table,such as n++GaAs. Layer 220 may then be capped with a layer of metal (notshown) of a thickness ranging from 100 angstroms to 2000 angstroms. Themetal layer may comprise Al, TiAu or any suitable metal. The metal layerserves to aid in absorption of infrared radiation and provides forenhanced ohmic contact to layer 220.

[0087] QWIP 200 is coupled to CMOS device 222 via electrical connection224 to form a detector pixal structure 226. CMOS device 222 may comprisea device such as a MOSFET which is formed by conventional semiconductorprocessing as is well known and widely practiced in the semiconductorindustry. To enhance contact between QWIP 200 and CMOS device 222, ametal layer (not shown) may be deposited overlying layer 212 beforemultiple quantum wells structure 214 is deposited thereon. A pluralityof detector pixel structures which detect different wavelengths ofinfrared radiation may then be combined into a focal plane array whichproduces an image corresponding to the received infrared radiation.

[0088] It should be noted that the steps of epitaxially growing ordepositing the various layers includes epitaxially growing or depositinglayers by processes such as MBE, MOCVD, MEE, CVD, PVD, PLD, CSD and ALEas previously indicated with respect to the processing steps describedabove for fabricating the structures shown in FIGS. 1-3. Further,although the present invention has been described using aGaAs/Al_(x)Ga_(1−x)A QWIP structure, other alternate QWIP materialsystems may include but are not limited toIn_(x)Ga_(1−x)As/In_(x)Al_(1−x)As, In_(x)Ga_(1−x)As/InP, InGaAsP/InP,In_(x)Ga_(1−x)As/GaAs, GaAs/Ga_(x)In_(1−x)P and GaAs/Al_(x)In_(1−x)P.

[0089] In the foregoing specification, the invention has been describedwith reference to specific embodiments. However, one of ordinary skillin the art appreciates that various modifications and changes can bemade without departing from the scope of the present invention as setforth in the claims below. Accordingly, the specification and figuresare to be regarded in an illustrative rather than a restrictive sense,and all such modifications are intended to be included within the scopeof the present invention.

[0090] Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, solution to occur or become morepronounced are not to be constructed as critical, required, or essentialfeatures or elements of any or all of the claims. As used herein, theterms “comprises,” “comprising,” or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but may include other elements not expresslylisted or inherent to such process, method, article, or apparatus.

I claim:
 1. A quantum well infrared photodetector element comprising: amonocrystalline substrate; a first layer comprising an accommodatingbuffer layer epitaxially grown overlying the substrate; a second layercomprising monocrystalline material overlying the first layer; a thirdlayer comprising monocrystalline material overlying the second layer; amultiple quantum well structure disposed adjacent the third layer; and afourth layer comprising monocrystalline material overlying the multiplequantum well structure.
 2. The quantum well infrared photodetectorelement of claim 1 further comprising an integrated circuit, wherein atleast a portion of the integrated circuit is formed in the substrate andis electrically coupled to the quantum well infrared photodetectorelement.
 3. The quantum well infrared photodetector element of claim 1,further comprising an amorphous oxide layer underlying the first layer.4. The quantum well infrared photodetector element of claim 1, whereinthe substrate comprises silicon.
 5. The quantum well infraredphotodetector element of claim 1, wherein the first layer comprises anoxide selected from the group consisting of alkali earth metaltitanates, alkali earth metal zirconates, alkali earth metal hafnates,alkali earth metal tantalates, alkali earth metal ruthenates, alkaliearth metal niobates, and perovskite oxides.
 6. The quantum wellinfrared photodetector element of claim 1, wherein the first layercomprises Sr₂Ba_(1−z)TiO₃ where z ranges from 0 to
 1. 7. The quantumwell infrared photodetector element of claim 1, wherein the second layercomprises a compound semiconductor material selected from the groupconsisting of GaAs, AlGaAs, InP, InGaAs, InGaP, ZnSe and ZnSeS.
 8. Thequantum well infrared photodetector element of claim 1, wherein thethird layer comprises an impurity doped compound semiconductor materialselected from the group consisting of GaAs, Al_(x)Ga_(1−x)As, InP,In_(x)Ga_(1−x)As, In_(x)Ga_(1−x)P, ZnSe and ZnSeS.
 9. The quantum wellinfrared photodetector element of claim 1, wherein the multiple quantumwell structure comprises alternating active layers and barrier layers,wherein the active layers comprise materials selected from the groupconsisting of GaAs, In_(x)Ga_(1−x)As, and InGaAsP, and the barrierlayers comprise materials selected from the group consisting ofAl_(x)Ga_(1−x)As, In_(x)Ga_(1−x)As, InP, GaAs, In_(x)Ga_(1−x)P, andAl_(x)In_(1−x)P, where x ranges from approximately 0 to
 1. 10. Thequantum well infrared photodetector element of claim 1, wherein thefourth layer comprises an impurity doped compound semiconductor materialselected from the group consisting of GaAs, Al_(x)Ga_(1−x)As, InP,In_(x)Ga_(1−x)As, In_(x)Ga_(1−x)P, ZnSe and ZnSeS, where x ranges from 0to
 1. 11. The quantum well infrared photodetector element of claim 1,further comprising a metal layer overlying the fourth layer.
 12. Thequantum well infrared photodetector element of claim 1, furthercomprising a fifth layer positioned between the first layer and thesecond layer, wherein the fifth layer comprises an additional bufferlayer.
 13. The quantum well infrared photodetector element of claim 1,further comprising a template layer positioned between the first layerand the second layer.
 14. The quantum well infrared photodetectorelement of claim 13, wherein the template layer comprises a Zintl-typephase material.
 15. The quantum well infrared photodetector element ofclaim 14, wherein the Zintl-type phase material comprises at least oneof SrAl₂, (MgCaYb)Ga₂, (Ca, Sr, Eu, Yb) In₂, BaGe₂As, and SrSn₂As₂. 16.The quantum well infrared photodetector element of claim 13, wherein thetemplate layer comprises a surfactant material.
 17. The quantum wellinfrared photodetector element of claim 16, wherein the surfactantmaterial comprises at least one of Al, In, and Ga.
 18. The quantum wellinfrared photodetector element of claim 16, wherein the template layerfurther comprises a capping layer.
 19. The quantum well infraredphotodetector element of claim 18, wherein the capping layer is formedby exposing the surfactant material to a cap-inducing material.
 20. Thequantum well infrared photodetector element of claim 19, wherein thecap-inducing material comprises at least one of As, P, Sb, and N. 21.The quantum well infrared photodetector element of claim 18, wherein thesurfactant comprises Al, the capping layer comprises Al₂Sr and thesecond layer comprises GaAs.
 22. The quantum well infrared photodetectorelement of claim 1, wherein the first layer comprises a monocrystallineoxide.
 23. The quantum well infrared photodetector element of claim 22,wherein the first layer comprises an oxide formed as a monocrystallineoxide which is subsequently heat treated to convert at least a portionof the monocrystalline oxide to an amorphous oxide.
 24. The quantum wellinfrared photodetector element of claim 22, wherein the monocrystallinesubstrate is characterized by a first lattice constant and the firstlayer is characterized by a second lattice constant different than thefirst lattice constant.
 25. The quantum well infrared photodetectorelement of claim 24, wherein the second layer is characterized by athird lattice constant different than the second lattice constant. 26.The quantum well infrared photodetector element of claim 22, wherein themonocrystalline substrate is characterized by a first crystallineorientation and the monocrystalline oxide is characterized by a secondcrystalline orientation and, wherein the second crystalline orientationis rotated with respect to the first crystalline orientation.
 27. Aprocess for fabricating a quantum well infrared photodetector comprisingthe steps of: providing a monocrystalline substrate; epitaxially growinga first layer comprising an accommodating buffer layer overlying thesubstrate; epitaxially growing a second layer comprising amonocrystalline material overlying the first layer; epitaxially growinga third layer comprising a monocrystalline material overlying the secondlayer; forming a multiple quantum well structure adjacent the thirdlayer; and growing a fourth layer comprising a monocrystalline materialoverlying the multiple quantum well structure.
 28. The process of claim27, further comprising forming at least a portion of an integratedcircuit in the substrate and electrically coupling the quantum wellinfrared photodetector to the integrated circuit.
 29. The process ofclaim 27, wherein providing a monocrystalline substrate comprisesproviding a substrate comprising silicon.
 30. The process of claim 27,further comprising forming an amorphous oxide layer underlying the firstlayer during the step of epitaxially growing the first layer.
 31. Theprocess of claim 27, wherein epitaxially growing a first layer comprisesepitaxially growing a monocrystalline oxide layer comprising an oxideselected from the group consisting of alkali earth metal titanates,alkali earth metal zirconates, alkali earth metal hafnates, alkali earthmetal tantalates, alkali earth metal ruthenates, alkali earth metalniobates and perovskite oxides.
 32. The process of claim 31, furthercomprising annealing the monocrystalline oxide layer to convert themonocrystalline oxide layer to an amorphous oxide layer, the annealingbeing carried out after at least the epitaxially growing a second layercomprising a monocrystalline material.
 33. The process of claim 27,wherein each of the steps of epitaxially growing comprises the step ofepitaxially growing by a process selected from the group consisting ofMBE, MOCVD, MEE, CVD, PVD, PLD, CSD and ALE.
 34. The process of claim27, wherein epitaxially growing a first layer comprises epitaxiallygrowing a monocrystalline layer comprising Sr_(z)Ba_(1−z)TiO₃, where zranges from 0 to
 1. 35. The process of claim 27, wherein epitaxiallygrowing a second layer comprising a monocrystalline material comprisesepitaxially growing a second layer comprising a compound semiconductormaterial selected from the group consisting of GaAs, AlGaAs, InP,InGaAs, InGaP, ZnSe and ZnSeS.
 36. The process of claim 27, whereinepitaxially growing a third layer comprising a monocrystalline materialcomprises epitaxially growing a third layer comprising a compoundsemiconductor material selected from the group consisting of GaAs,Al_(x)Ga_(1−x)As, InP, In_(x)Ga_(1−x)As, In_(x)Ga_(1−x)P, ZnSe and ZnSeSwhere x ranges from 0 to
 1. 37. The process of claim 36, furthercomprising the step of impurity doping the third layer.
 38. The processof claim 27, wherein forming a multiple quantum well structure furthercomprises forming alternating active layers and barrier layers, whereinthe active layers comprise materials selected from the group consistingof GaAs, In_(x)Ga_(1−x)As, and InGaAsP and the barrier layers comprisematerials selected from the group consisting of Al_(x)Ga_(1−x)As,In_(x)In_(1−x)As, InP, GaAs, In_(x)Ga_(1−x)P and Al_(x)In_(x−x)P, wherex ranges from 0 to
 1. 39. The process of claim 27, wherein epitaxiallygrowing a fourth layer comprising a monocrystalline material comprisesepitaxially growing a fourth layer comprising a compound semiconductormaterial selected from the group consisting of GaAs, Al_(x)Ga_(1−x)As,InP, In_(x)Ga_(1−x)As, In_(x)Ga_(1−x)P, ZnSe and ZnSeS.
 40. The processof claim 39, further comprising impurity doping the fourth layer. 41.The process of claim 27, further comprising growing a metal layeroverlying the fourth layer.
 42. The process of claim 27, furthercomprising epitaxially growing a fifth layer before epitaxially growingthe second layer, wherein the fifth layer comprises an additional bufferlayer.
 43. The process of claim 27, further comprising forming atemplate layer before epitaxially growing the second layer.
 44. Theprocess of claim 43, wherein forming a template layer comprises forminga template layer comprising a Zintl-type phase material.
 45. The processof claim 44, wherein forming a template layer comprising a Zintl-typephase material comprises forming a template layer of Zintl-type phasematerial selected from the group comprising SrAl₂, (Mg, Ca, Yb) Ga₂,(Ca, Sr, Ev, Yb) In₂, BaGe₂As, and SrSn₂As₂.
 46. The process of claim43, wherein forming a template layer comprises forming a template layercomprising surfactant material.
 47. The process of claim 46, whereinforming a template layer comprising surfactant material comprisesforming a template layer comprising surfactant material formed of atleast one of Al, In, and Ga.
 48. The process of claim 46, whereinforming a template layer further comprises forming a template layerhaving a capping layer.
 49. The process of claim 48, wherein forming atemplate layer having a capping layer comprises exposing the surfactantmaterial to a cap-inducing material.
 50. The process of claim 49,wherein exposing the surfactant material to a cap-inducing materialcomprises exposing the surfactant material to at least one of As, P, Sb,and N.
 51. The process of claim 27, wherein said process of epitaxiallygrowing a first layer comprises growing a monocrystalline oxide layer.52. The process of claim 27, wherein growing a first layer comprisesgrowing a monocrystalline oxide layer and subsequently heating saidmonocrystalline oxide layer to convert the monocrystalline oxide layerto an amorphous oxide layer.
 53. The process of claim 51, whereinproviding a monocrystalline substrate comprises providing amonocrystalline substrate characterized by a first lattice constant, andwherein growing a monocrystalline oxide layer comprises growing a firstlayer characterized by a second lattice constant which is different thanthe first lattice constant.
 54. The process of claim 53, whereinepitaxially growing a second layer comprises growing a second layercharacterized by a third lattice constant which is different than thesecond lattice constant.
 55. The process of claim 51, wherein providinga monocrystalline substrate comprises providing monocrystallinesubstrate characterized by a first crystalline orientation and growing amonocrystalline oxide layer comprises growing a monocrystalline oxidelayer characterized by a second crystalline orientation and, wherein thesecond crystalline orientation is rotated with respect to the firstcrystalline orientation.
 56. A quantum well infrared photodetectorcircuit comprising: a monocrystalline silicon substrate; a portion of anMOS circuit formed in the silicon substrate; a first layer ofmonocrystalline oxide material selected from the group consisting ofalkali earth metal titanates, alkali earth metal zirconates, alkaliearth metal hafnates, alkali earth metal tantalates, alkali earth metalruthenates, alkali earth metal niobates, and perovskite oxides; anamorphous silicon oxide strain relief layer formed between themonocrystalline oxide layer and the silicon substrate; a second layer ofmonocrystalline material selected from the group consisting of GaAs,AlGaAs, InP, InGaAs, InGaP, ZnSe and ZnSeS overlying the first layers; athird layer of impurity doped monocrystalline material selected from thegroup consisting of GaAs, Al_(x)Ga_(1−x)As, InP, In_(x)Ga_(1−x)As,In_(x)Ga_(1−x)P, ZnSe and ZnSeS where x ranges from 0 to 1; a multiplequantum well structure disposed adjacent said third layer; a fourthlayer of impurity doped monocrystalline material selected from the groupconsisting of GaAs, Al_(x)Ga_(1−x)As, InP, In_(x)Ga_(1−x)As,In_(x)Ga_(1−x)P, ZnSe and ZnSeS where x ranges from 0 to 1; anelectrical connection electrically coupling the portion of an MOScircuit and the multiple quantum well structure.
 57. The quantum wellinfrared photodetector circuit of claim 56, wherein the first layercomprises Sr_(z)Ba_(1−z)TiO₃ where z ranges from 0 to
 1. 58. The quantumwell infrared photodetector circuit of claim 56, wherein the multiplequantum well structure comprises alternating active layers and barrierlayers, wherein the active layers comprise materials selected from thegroup consisting GaAs, In_(x)Ga_(1−x)As, and InGaAsP, where x rangesfrom approximately 0 to 1, and the barrier layers comprise materialsselected from the group consisting of Al_(z)Ga_(1−z)As,In_(z)Ga_(1−z)As, InP, GaAs, In_(z)Ga_(1−z)P, and Al_(z)In_(1−z)P, wherez ranges from approximately 0 to
 1. 59. The quantum well infraredphotodetector circuit of claim 56, further comprising a metal layeroverlying the fourth layer.
 60. The quantum well infrared photodetectorcircuit of claim 56, further comprising a fifth layer positioned betweenthe first layer and the second layer, wherein the fifth layer comprisesan additional buffer layer.
 61. The quantum well infrared photodetectorcircuit of claim 56 further comprising a template layer positionedbetween the first layer and the second layer.
 62. The quantum wellinfrared photodetector circuit of claim 61, wherein the template layercomprises a Zintl-type phase material.
 63. The quantum well infraredphotodetector circuit of claim 62, wherein the Zintl-type phase materialcomprises at least one of SrAl₂, (MgCaYb)Ga₂, (Ca, Sr, Eu, Yb) In₂,BaGe₂As, and SrSnAs₂.
 64. The quantum well infrared photodetectorcircuit of claim 61, wherein the template layer comprises a surfactantmaterial.
 65. The quantum well infrared photodetector circuit of claim64, wherein the surfactant comprises at least one of Al, In, and Ga. 66.The quantum well infrared photodetector circuit of claim 64, wherein thetemplate layer further comprises a capping layer.
 67. The quantum wellinfrared photodetector circuit of claim 66, wherein the capping layer isformed by exposing the surfactant material to a cap-inducing material.68. The quantum well infrared photodetector circuit of claim 67, whereinthe cap-inducing material comprises at least one of As, P, Sb and N. 69.The quantum well infrared photodetector circuit of claim 66, wherein thesurfactant material comprises Al, the capping layer comprising Al₂Sr andthe second layer comprises GaAs.